Wireless microphones are used to transmit sound to an amplifier or recording device without need of a physical cable. They are used for many functions, including, for example, enabling broadcasters and other video programming networks to perform electronic news gathering (ENG) activities at locations in the field and the broadcasting of live sports events. Wireless microphones are also used in theaters and music venues, film studios, conventions, corporate events, houses of worship, major sports leagues, and schools.
Typically, wireless microphone systems include a microphone that is, for example, a handheld unit, a body-worn device, or an in-ear monitor; a transmitter (e.g., either built into the handheld microphone or in a separate “body pack” device) comprising one or more antennas; and a remote receiver comprising one or more antennas for communicating with the transmitter. The antennas included in the microphone transmitter and receiver can be designed to operate in certain spectrum band(s), and may be designed to cover either a discrete set of frequencies within the spectrum band or an entire range of frequencies in the band. The spectrum band in which the microphone operates can determine which technical rules and/or government regulations apply to that microphone system. For example, the Federal Communications Commission (FCC) allows the use of wireless microphones on a licensed and unlicensed basis, depending on the spectrum band.
Most wireless microphones that operate today use spectrum within the “Ultra High Frequency” (UHF) bands that are currently designated for television (TV) (e.g., TV channels 2 to 51, except channel 37). Currently, wireless microphone users need a license from the FCC in order to operate in the UHF/TV bands (e.g., 470-698 MHz). However, the amount of spectrum in the TV bands available for wireless microphones is set to decrease once the FCC conducts the Broadcast Television Incentive Auction. This Auction will repurpose a portion of the TV band spectrum—the 600 MHz—for new wireless services, making this band no longer available for wireless microphone use. Wireless microphones can also be designed for operation in the currently licensed “Very High Frequency” (VHF) bands, which cover the 30-300 MHz range.
An increasing number of wireless microphones are being developed for operation in other spectrum bands on an unlicensed basis, including, for example, the 902-928 MHz band, the 1920-1930 MHz band, and the 2.4 GHz band (also known as the “ZigBee” band). However, given the vast difference in frequency between, for example, the UHF/TV bands and the ZigBee band, wireless microphone systems that are specifically designed for one of these two spectrums typically cannot be repurposed for the other spectrum without replacing the existing antenna(s).
Moreover, antenna design considerations can limit the number of antennas that are included within a single device (e.g., due to a lack of available space), while aesthetic design considerations can restrict the type of antennas that can be used. For example, whip antennas are traditionally good performers and by virtue of its external design, take up very little internal device space. However, these antennas can be expensive, distracting (for example, during a performance), and aesthetically unappealing, especially when they are long in length. As another example, handheld microphones typically include a reduced-size antenna that is integrated into the microphone housing to keep the overall package size small and comfortable to use. However, this limitation in antenna size/space makes it difficult for the handheld microphone to provide sufficient radiated efficiency.
More specifically, existing solutions for reduced-sized, broadband antennas include placement of a helical antenna within a housing of the handheld microphone, for example, as shown and described in U.S. Pat. Nos. 7,301,506 and 8,576,131, both of which are incorporated herein by reference in their entirety. In both cases, the helical antenna assembly includes an antenna tape wrapped around a dielectric core to form a single or double helix structure and the pitch, width, and/or length of the antenna tape is adjusted to obtain desired electrical characteristics. However, these existing antenna solutions are ineffective for use in broadband and multiband antenna operations.
Accordingly, there is a need for a wireless microphone system that can adapt to changes in spectrum availability, but still provide consistent, high quality, broadband performance with a low-cost, aesthetically-pleasing design.